Accurate determination of the optical properties (the absorption coefficient μa and the reduced scattering coefficient μs′) of tissues is very important in a variety of diagnostic and therapeutic procedures. Optical diffusion theory is frequently used as the forward model for describing the photon transfer in media with large reduced albedos (a ′ ) and in large source-detector separations (SDS). Several other methods (PN approximation, hybrid diffusion-P3 approximation) have also been published that describe photon transfer in media with low a ′ or small SDSs. We studied the theoretical models for the steady-state spatially resolved diffuse reflectance measurement to accurately determine μa and μs′ at large a ′ range but small SDSs. Instead of using a single model, a joint derivation method is proposed. The developed method uses one of the best aforementioned theoretical methods separately in five ranges of a ′ determined from several forward models. In the region of small SDSs (the range between 0.4 and 8 mm) and large a ′ range (between 0.5 and 0.99), the best theoretical derivation model was determined. The results indicate that the joint derivation method can improve the derivation accuracy and that a ′ range can be determined by the steady-state spatially resolved diffuse reflectance measurement.
In the research of optical diagnosis, such as noninvasive measurement of blood glucose by near-infrared
diffuse-reflectance spectroscopy, the fiber-optic probe are widely used to deliver light to the interested tissue site and
collect the light from the tissue. In order to minimize motion artifacts and specula reflectance, the fiber-optic probe
contact to tissue site with certain pressure. The spacing between tissue components decreased due to water displacement,
while the volumes of cells and elastic fibers are reduced which in turn increase the concentration of the scatter and
absorber inside the tissue. In our research a three-layer skin model is established and the Finite Element Method is
employed to simulate the deformation of skin tissue caused by fiber-optic probe with different pressure. The change of
water volume inside the tissue as well as the concentration and scattering cross section of scatters are considered. The
Monte Carlo simulation is utilized to establish the diffuse-reflectance spectroscopy of three-layer skin model before and
after compression. The result indicated that the pressure of fiber-optics probe should be controlled less the 50kpa to
reduce the influence on measurement.
This paper discusses light propagation in N-layered turbid media. The hybrid diffusion-P3 equation is solved for an N-layered finite or infinite turbid medium in the steady-state domain for one point source using the extrapolated boundary condition. The Fourier transform formalism is applied to derive the analytical solutions of the fluence rate in Fourier space. Two inverse Fourier transform methods are developed to calculate the fluence rate in real space. In addition, the solutions of the hybrid diffusion-P3 equation are compared to the solutions of the diffusion equation and the Monte Carlo simulation. For the case of small absorption coefficients, the solutions of the N-layered diffusion equation and hybrid diffusion-P3 equation are almost equivalent and are in agreement with the Monte Carlo simulation. For the case of large absorption coefficients, the model of the hybrid diffusion-P3 equation is more precise than that of the diffusion equation. In conclusion, the model of the hybrid diffusion-P3 equation can replace the diffusion equation for modeling light propagation in the N-layered turbid media for a wide range of absorption coefficients.
Non-invasive blood glucose monitoring using NIR light has been suffered from the variety of optical background that is
mainly caused by the change of human body, such as the change of temperature, water concentration, and so on. In
order to eliminate these internal influence and external interference a so called floating-reference method has been
proposed to provide an internal reference. From the analysis of the diffuse reflectance spectrum, a position has been
found where diffuse reflection of light is not sensitive to the glucose concentrations. Our previous work has proved the
existence of reference position using diffusion equation. However, since glucose monitoring generally use the NIR light
in region of 1000-2000nm, diffusion equation is not valid because of the high absorption coefficient and small source-detector
separations. In this paper, steady-state high-order approximate model is used to further investigate the existence
of the floating reference position in semi-infinite medium. Based on the analysis of different optical parameters on the
impact of spatially resolved reflectance of light, we find that the existence of the floating-reference position is the result
of the interaction of optical parameters. Comparing to the results of Monte Carlo simulation, the applicable region of
diffusion approximation and higher-order approximation for the calculation of floating-reference position is discussed at
the wavelength of 1000nm-1800nm, using the intralipid solution of different concentrations. The results indicate that
when the reduced albedo is greater than 0.93, diffusion approximation results are more close to simulation results,
otherwise the high order approximation is more applicable.
The estimate of tissue optical properties is an important challenge in biomedical science. In the research of
precancerous diagnosis and glucose concentration detection, the accuracy of chromospheres concentrations
measurement depends on the measurement of absorption coefficient. So determining the absorption coefficient
accurately is crucial both in vivo and in vitro. The
Double-Integrating-Spheres (DIS) system is widely used in
measuring optical properties of tissue. As there are light losses, sphere alters and cross talk in the measurement with
DIS system, the estimating error of the optical properties increases, especially for absorption coefficient. Based on the
DIS setup, the Monte Carlo simulation and principle of the integrating sphere are applied to investigate the effects of
light loss and cross talk with various parameters of sample. According to the investigation, a fast correcting method is
introduced to modify the measuring results. After a calibration dataset was employed, the algorithm based on artificial
neutral network is applied to modify the measurement with DIS system. The modified results indicate that the
reconstruction accuracy of absorption coefficient is fully improved compared with the uncorrected ones.
A reference position where the diffuse reflectance light intensity is insensitive to the variation of glucose concentration
exists in the radial detection space for glucose measurement in the scattering medium such as skin. The signal measured
in this position could be used as an inside reference to evaluate the influence on spectrum caused by other interferential
factors. The relationship between the position of radial reference point and the skin tissue property is studied in this paper.
Three-layer skin models with different optical parameters are designed to get sample sets at 1200~1700nm. In these
sets, μa, μs and g of dermis varies respectively, so does the depth of epidermis or dermis. The distribution rule of
dispersion of diffuse reflectance light intensity in the radial space is confirmed with the glucose concentration changes.
And the distribution property of the radial reference position in every sample set is obtained through Monte Carlo
simulation. The result shows that the distance of radial reference position from light source is insensitive to the variation
of absorption coefficient or the depth of dermis, but an increased scattering coefficient will shorten the distance; an
increased anisotropy coefficient or depth of epidermis will lengthen it. On the basis of that, the optical probes with
different structures are designed according to the skin tissue properties. So they could be used for the measurement of
corresponding patients, which enhances the practicability of floating reference method greatly.
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